>63 % efficiency: (R)evolution in turbine technology 

With its new HL-class gas turbines, Siemens is pushing the limits for efficiency, performance and flexibility even further. But owners of the existing fleet of Siemens turbines will profit from this leap in innovation, too.


by Moritz Gathmann

In a huge production hall in the western part of Berlin, not far from the cradle of Siemens, hundreds of employees are working on some of the most powerful gas turbines the world has ever known. Blades are inserted into turbine modules and gas turbines are assembled with the utmost accuracy.


With more than 80 units sold worldwide and over 450,000 operating hours under its belt, Siemens’ SGT-8000H series has proven to be the most reliable gas turbine in its class. Now, Siemens is taking the next step: Based on the proven H-class technology, it developed a gas turbine that pushes the efficiency threshold from 61 to more than 63 percent. In the midst of this well-organized, buzzing hive, Zuozhi Zhao explains passionately how he and his team made this technology leap possible.

Rapid prototyping and additive manufacturing

The China-born engineer in his mid-40s is the Chief Technology Officer (CTO) of the Division Power and Gas at Siemens. His office is located a stone’s throw from the historic production hall, a masterpiece of industrial architecture that has been continuously used for the same purpose for more than 100 years – assembling turbines. Against this backdrop of local industrial history, it is obvious how times have changed: The innovations he is talking about have been conceived in close collaboration with engineers from all over the world at greater innovation speed. Rapid prototyping – the design process backed by 3D printing, which speeds up component testing – took place in Berlin and at the company’s Clean Energy Center in Ludwigsfelde, as did the thorough testing phase. Now, the turbine will be validated under real conditions thousands of miles away from Berlin in a technology partnership with Duke Energy at its Lincoln County site in North Carolina, USA. “That’s what it means to work in a global company,” says Zhao with a smile.

Technology that withstands the heat

The HL-class’ combined cycle efficiency of over 63 percent is impressive. “In order to increase efficiency and improve performance, gas turbines have to be operated at even higher combustion temperatures – that’s the key,” explains Zhao. “We identified five levers to make higher firing temperatures possible.” Thus, his team developed an advanced combustion system that allows for higher firing temperatures, and at the same time more operational flexibility. Innovative, heat-resistant multi-layer coatings have been used to protect the blade material against the increased heat. But for the blades, Zhao points out, the inner values prove just as important: Superefficient internal cooling features have been engineered to improve the cooling process and hence efficiency. Furthermore, optimized sealing minimizes the leakage of cooling air. Finally, evolutionary 3D blading improved the compressor’s aero-efficiency.


Following this technology leap, is it time to take a rest? “On the contrary!” Ever the restless innovator, the CTO explains that, in the meanwhile, Siemens has already set its sights on the new threshold of 65 percent efficiency. “Speed in technology development is driven by digitalization, by additive manufacturing, by better collaboration,” he says. “And it has been rapidly gaining momentum: It took us ten years to break the 60 percent efficiency barrier, then another six years to improve to 61.5 percent. Now we’re taking the next step to 63 percent and beyond in under two years.” But as Zhao knows well, for Siemens’ customers, it’s not only about speed and efficiency – the solutions have to be above all reliable and cost-effective.

A clean future for gas turbines

Talking about customers: Does it make sense to improve gas turbines even further if the world is turning more and more to renewables as sources of energy? Zhao doesn’t see any contradiction. “The sun is not always shining, and the wind is not always blowing. That’s why you need to compensate shortages,” says Zhao. The ramp-up rate of the HL-class turbines can go up to 85 megawatts per minute. That’s crucial if energy is needed urgently. “If you look at the power you can generate and the space you’ll need to do it – the power density – there’s nothing that could compete with a gas turbine,” says Zhao.

If you look at power density, there’s nothing that could compete with a gas turbine.
Zuozhi Zhao, CTO Power and Gas, Siemens

“In the future, efficient turbines could also be fired with gas that comes from renewable energy,” he explains. Nowadays, a lot of wind or solar energy is basically wasted because it cannot be stored – at least not for a long time. One option could be to turn it into methane or hydrogen, and use this stored energy to fuel a gas-fired power plant when needed. Whatever the solution, Siemens is already prepared for the future, Zhao points out: “Our gas turbines are highly fuel flexible and can run on natural gas as well as other synthetic fuels.”

Fleet performance boosted by data analytics based on design and operations know-how

The turbines are also designed to plug into Siemens’ digital offering for plant operators and utilities, incorporating connectivity to MindSphere, the cloud-based Siemens operating system for the Internet of Things. It offers performant analytics instruments. “The three powerful pillars of this operating system are design know-how, data know-how, and operations know-how,” says Zhao. “And by combining them through MindSphere, our customers will have a tremendous benefit. It can tell the customer how he operates, by when he should replace certain parts in order to have the highest reliability and how he can reduce fuel consumption.”

By combining design, data, and operations know-how through MindSphere, our customers will have a tremendous benefit.
Zuozhi Zhao, CTO Power and Gas, Siemens

In further good news, the innovations of the new gas turbine will not only yield benefits to HL-class owners. “In the near future, all customers will be offered solutions to raise their efficiency, performance and flexibility – by upgrading new components and technology to the entire fleet,” stresses Zhao. “What you cannot change are all the casing parts. But everything else, starting with the blades, can be changed. This approach of modularization and standardization is just one of a series of levers that we are using to help our customers compete in a rapidly changing market.” And apart from replacing hardware, existing turbines can of course also plug into MindSphere in order to boost a power plant’s efficiency.


Moritz Gathmann is a journalist based in Berlin.

Picture credits: Tobi Bohn

The new Siemens HL-class consists of three engines: SGT5-9000HL, SGT6-9000HL and SGT5-8000HL. In simple-cycle operation the air-cooled SGT-9000HL gas turbine will provide a capacity of 545 megawatts for the 50-Hertz market and 374 megawatts in the 60-Hertz version. The SGT5-8000HL will provide 453 megawatts in simple-cycle operation. All engines are designed to reach more than 63 percent combined cycle efficiency.

Dr. Zhao joined Siemens in March 2009, holding various executive positions in gas turbine technology and operation within the Power and Gas Division in China prior to his appointment as CTO of Power and Gas in January 2017.

He earned his PhD in Mechanical and Aerospace Engineering from Arizona State University and holds a BS and MS in Mechanical Engineering from Tsinghua University in Beijing.

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